The present invention relates to an improvement in a coaxial type starter device comprising a motor section constituted by a d.c. motor, an electromagnetic switch and a driving force transmitting unit comprising a speed reducing mechanism and an overrunning clutch, which are arranged in the same axial line.
It has been known to use a starter in which a battery is used for a source of power as a device for rotating an engine by an external force when the engine is to be started. As a type of this kind of starter, it has been known to use a coaxial type starter device wherein a motor section constituted by a d.c. motor is arranged in the same axial line as an electromagnetic switch for urging the rotary output shaft of the starter in its axial direction to thereby connect a pinion provided at an end of the rotary output shaft with a ring gear of the engine or to disconnect the pinion from the ring gear, and a driving force transmitting unit comprising a planet gear wheel type speed reducing mechanism. Further, an overrunning clutch is disposed in front of the motor section.
FIG. 4 shows a conventional coaxial type starter device of the above-mentioned type. The coaxial type starter device comprises a yoke 1 defining the outer wall of the starter and adapted to form a magnetic circuit. An armature 2 for producing a revolutional force is disposed in the yoke 1. The yoke 1 and the armature 2 constitute elements in the motor section of the starter. An armature rotary shaft 2a as the core of the armature 2 is in a tubular form, and a sun gear 10a which is an element of the planet gear wheel type speed reducing mechanism 10 is formed at an end portion (at the front side) of the outer circumference of the armature rotary shaft 2a. A rotary output shaft is inserted rotatably in the tubular armature rotary shaft 2a from its front side. A pinion 4 to be engaged with a ring gear (not shown) of the engine is fixed to the front end portion of the rotary output shaft 3 and a helical spline 5 is formed at the outer circumference of the rotary output shaft 3 at a position between the pinion 4 and the sun gear 10a at the front end of the armature rotary shaft 2a in which the rotary output shaft is partially inserted.
An electromagnetic switch 6 for urging the rotary output shaft 3, by an attracting force due to an electromagnetic force, in the direction that the pinion 4 is brought to engagement with the ring gear, is provided at the rear of the armature rotary shaft 2a. The front part of the rotary output shaft 3 is supported by a gear case 8 by means of a roller bearing 7 and the rear part of it receives a support in the tubular armature rotary shaft 2a by means of a slide bearing 9. There are provided in the gear case 8 the above-mentioned planet gear wheel type speed reducing mechanism 10 and the overrunning clutch 11 to constitute the driving force transmitting unit. The overrunning clutch 11 is constituted by a clutch outer member 11a, rollers 11b disposed inside thereof and a clutch inner member 11c. The clutch inner member 11c has a helical spline portion at its inner circumference which is adapted to mesh with the above-mentioned spline 5 formed at the outer circumference of the rotary output shaft 3. Further, the clutch outer member 11a is provided with holes in which pins 12 for supporting planet gear wheels 10b as a structural element of the planet gear wheel type speed reducing mechanism 10 are forcibly inserted.
An internal gear 10c meshing with the planet gear wheels 10b is formed in the gear case 8. The sun gear wheel 10a, the planet gear wheels 10b and the internal gear 10c constitute the above-mentioned speed reducing mechanism 10.
In the conventional coaxial type starter device having the above-mentioned construction, when a starter switch (not shown) is operated to start the engine, an electric current is supplied from a battery (not shown) to the electromagnetic switch 6; the plunger (not shown) in the electromagnetic switch 6 is attracted so that the rotary output shaft 3 is fowardly pushed, whereby the pinion 4 is brought to mesh with the ring gear (not shown) of the engine. On the other hand, upon attracting the plunger, contacts installed in the electromagnetic switch 6 are made and an electric current is supplied from a battery to the armature 2 so that a force of revolution is produced. The force of revolution is transmitted to the rotary output shaft 3 via the planet gear wheel type speed reducing mechanism 10 and the overrunning clutch 11, and it is further transmitted to the ring gear of the engine through the pinion 4 attached to the rotary output shaft 3, whereby the engine is started.
In the conventional coaxial type starter device having the construction described above, the positions of the holes 13 formed in the clutch outer member 11a, in which the pins for supporting the planet gear wheels are forcibly inserted, are determined without consideration of their positions with respect to wedge-like spaces formed in the clutch outer member 11a. Accordingly, the holes 13 cannot be formed as through holes extending in the axial direction of the clutch outer member. Accordingly, it was difficult to obtain accurate holes by machining operations. In the case of forming the holes 13 by a cold forging method, it was difficult to form the holes together with the wedge-like spaces by a single stamping operation. Accordingly, when the holes 13 are formed separate from the wedge-like spaces, it was inavoidable that the deviation of the holes 13 with respect to the wedge-like spaces took place.
The conventional coaxial type starter device is not of such structure that strict attention is paid to coaxial arrangement between the clutch outer member 11a of the overrunning clutch 11 and the armature rotary shaft 2a. Accordingly it was inavoidable that there occured deviation between the armature rotary shaft 2a and the wedge-like spaces of the overrunning clutch 11 or the pins 12 for supporting the planet gear wheels 10b. This caused generation of abnormal noises and a reduction in the service life.